Aluminum nitride has a band gap of 6.2 eV and a high thermal conductivity, so that it is excellent as a substrate material for a light emitter (LED, LD) in the ultra-violet region and for an electronic device. The development of a production technique of producing a semiconductor wafer has been desired. Until now, production techniques of AlN single crystal such as sublimation and HVPE methods have been proposed. A technique of producing AlN according to flux method (solution method) was disclosed in Japanese patent publication 2003-119099A and “Mat. Res. Bull.” Vol. 9 (1974), pages 331 to 336. A transition metal is used as a flux in Japanese patent publication 2003-119099A. An AlN single crystal is obtained from Ca3N2 and AlN powder in “Mat. Res. Bull.” Vol. 9 (1974), pages 331 to 336.
It has recently been reported that bulk gallium nitride single crystal of a high quality can be synthesized at a relatively low temperature and a low pressure by using Na as a catalyst (Japanese patent publication 2000-327495A). The raw materials are gallium and sodium azide.
Further, according to “Phys. Stat. Sol.” Vol. 188 (2001) pages 415 to 419, a crystal of an AlGaN solid solution (size: 300 to 500 microns, composition; Al0.22Ga0.78N) were successfully grown at a pressure of about 100 to 110 atms (10 to 11 MPa) from 750° C. to 800° C. using raw materials of sodium azide, gallium and aluminum.
According to prior art Japanese patent publication 2003-119099A, “Mat. Res. Bull.” Vol. 9 (1974), pages 331 to 336 and the like, an AlN single crystal having a large size and high quality (low defect density) has not been successfully grown. According to “Phys. Stat. Sol.” Vol. 188 (2001) pages 415 to 419, although single crystals have been successfully grown from an AlGaN solid solution containing a small amount of Al. An AlN single crystal is not described or suggested.